1.15.3. Levels

The instrument used for collecting the elevation measurements from the field are called levels. The purpose of a level instrument is to establish a horizontal line of sight in order to take the measurement to compute the elevations.

Levels are surveying instruments that are specifically designed to measure elevations accurately. They help in establishing a horizontal line of sight, which is crucial for accurate elevation readings. By ensuring that the line of sight is horizontal, surveyors can determine the height difference between points accurately.

Imagine you are trying to bake a cake, and you need to ensure the cake batter is spread evenly in the pan. If you tilt the pan, one side of the batter will be higher than the other, leading to an uneven cake. Similarly, levels help surveyors keep a 'flat' or even reference when measuring elevations—ensuring that construction projects like buildings or roads are straight and true.

The level consists of the following essential parts:

1. A telescopic tube which provides a line of sight.
2. A diaphragm (or cross-hairs) which holds the cross hairs (fitted near the eyepiece within telescope).
3. Eyepiece which is fitted at one end of telescope, and used to magnify the image formed in the plane of the diaphragm. The observer keeps one eye closer to it to read the staff reading during leveling. The eyepiece is fitted with a screw which is moved clockwise or anticlockwise to focus the diaphragm.
4. Objective lens, which is fitted at the other end of the telescope, is used to collect the incoming rays from the levelling staff (objects) that form the image inside the telescopic view.
5. A focusing screw which is used to focus the image at the cross hairs.
6. A level bubble tube which is attached to telescopic tube to make the line of sight horizontal.
7. A levelling head which supports the level instrument, and is fitted with a circular bubble tube, used for making the base of instrument approximately levelled.
8. A tripod for fixing the level instrument.

Each part of the level has a specific function. The telescopic tube allows the surveyor to look through and see a line of sight to the leveling staff. The diaphragm with cross-hairs helps in aligning the sight, while the eyepiece magnifies the image for clearer viewing. The objective lens collects light to form the image of the staff, and the focusing screw ensures that this image is sharp. The level bubble tube indicates when the instrument is level, and the levelling head supports the entire setup on a stable base provided by the tripod.

Think of a level like a camera. Just as a camera has a lens, a viewfinder, and adjustments to focus and level the shot, a level instrument has its own components working together to ensure clear and accurate height measurements. An improperly focused camera leads to blurry photos, much like an improperly focused level can lead to inaccurate height readings.

Various types of leveling instruments are: (a) Dumpy level (b) Tilting level (c) Engineers level (d) Automatic level (e) Digital level (f) Laser level

Levels come in different types, each with its unique features. The Dumpy level is straightforward and rigid, while the Tilting level can be inclined for easier observation. The Engineer's level is compact and lightweight, allowing for quick observations. The Automatic level automatically adjusts itself for leveling, and the Digital level provides digital readouts for accuracy. Finally, the Laser level uses laser technology for precise measurements over distances.

It’s like choosing the right tool for a job. If you're cooking, you might choose a frying pan for sautéing, a roasting pan for the oven, or a grill for barbecuing. Similarly, in leveling, surveyors choose different types of levels depending on the specific requirements of their task, whether it's accuracy, ease of use, or the environment in which they're working.

Auto levels are quick to level with greater accuracy which have made it more demanding amongst the surveyors. For general use, these are popular because of their ease and rapid operation, however, the reading is manually recorded. Digital levels have the provision of transferring the digital data to a computer where the measurements are processed to get the elevations, profiles or DEM.

Automatic levels save time by automatically leveling themselves, providing fast and accurate readings without the need for constant adjustment. Digital levels take it a step further by allowing data to be stored and transferred to computers, facilitating easier analysis and calculations of elevations, which is advantageous for larger projects.

Imagine a car that can park itself versus one that requires you to steer and adjust continuously. The automatic level is like the self-parking car; it simplifies the leveling process significantly. On the other hand, the digital level is like having a navigation system that not only tells you where to go but also remembers the routes and helps plan future trips.

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